How to get rid of fireflies caused by glass material?
Increase your clamping values.
Within Blender's render settings tab, there are two values: Clamp direct and Clamp indirect. In essence, a higher value for these will reduce fireflies at the cost of realism by lowering the values of very high intensity pixels. With your samples already at such a high value, a slight amount of increasing the clamping could definitely reduce your fireflies.
(side note: some of your fireflies appear to be a result of noise, you can try using the new denoise node in the compositor.)